Double Trigon is Trigon at twice the size: Double Klondike's hidden staircase, but the tableau builds down in suit rather than alternating colours. Two decks are dealt into nine columns of one to nine cards with only the tips turned, over a fifty-nine-card stock that turns one at a time with unlimited redeals. Runs travel, only a king may take an empty column, and eight foundations build up in suit. Bank all 104 cards to win.
Shuffle two decks together. Deal nine columns: one card in the first, two in the second, up to nine in the ninth. Only the top card of each column is face up; the thirty-six beneath are hidden. The remaining fifty-nine cards form the stock, and eight foundations wait above.
Building in suit halves the hosts for every card: a red seven in Klondike has two black eights to land on, but the seven of hearts here has only the eights of hearts — of which, with two decks, there are two. That second copy is the whole game.
Double Trigon is the in-suit member of the two-deck Klondike line, next to 8 x 8, Big Harp, Open Gargantua and Inquisitor. Trigon is Klondike built down in suit; Double Trigon doubles the deck and the foundations and lets the stock turn without limit. Inquisitor keeps the in-suit build but opens the deal, frees the spaces and turns three cards a time.
Double Trigon runs in your browser — free, no download, no sign-up. Install it as an app on your phone or computer and it works offline. You get unlimited undo, a hint button that names a legal move, statistics that track your wins and times, and seeded deals: every game has a seed you can replay, so a board you enjoyed (or lost) can be played again exactly.